1. Field of the Invention
The invention is in the field of keyboard apparatus for input of one character or function at a time and particularly of that type of apparatus which is responsive to imposition of a flexible conductive member, such as the operator's finger, to energize a selected combination of conductors to represent a selected character or function.
2. Discussion of the Prior Art
Modern integrated circuits can provide complex electronic devices which are low cost, small, and light weight. It can be expected that further developments will continue to increase complexity while reducing cost and size. In equipments requiring a keyboard, conventional keyboard apparatus may contribute substantially to the size and cost. In the case of pocket calculators and similar equipments, the cost and size limits are determined by the keyboard apparatus. The range of equipments which are practical will be expanded with reduction in size and cost of keyboard apparatus.
Mechanical switches having more than one pole are bulky and expensive, so conventional keyboards to provide codes representing characters or functions generally use single pole switches and encoding circuits. Each switch represents a character or function by energizing a lead going to the encoding circuit which then produces the desired binary or other code representation. The number of connections required between the keyboard and the encoding circuit is equal to the number of characters and functions.
The encoding circuitry could be included on the same integrated circuit chp as the utilizing apparatus with only a small addition to the cost of the chip for the added circuitry. A large number of pins would be required on the integrated circuit pack for connections between the keyboard and the encoding circuits on the chip. Each connection requires a considerable chip area and is presently made by hand labor so the cost for a large number of connections is considerable.
Present electronic equipments use circuits with a fast speed of response so they are susceptible to errors resulting from various types of keyboard transients. The prior art includes many systems designed to overcome the effects of key bounce and other keyboard transients and obtain proper entry of data.
Some electronic musical instruments play only one note at a time and can respond to only one operated playing key at a time. In U.S. Pat. No. 3,610,801, Fredkin and Minsky control the playing of such an instrument by providing a binary code to represent each note to be played. My U.S. Pat. No. 3,711,618 discloses apparatus which plays chords and bass along with a solo melody in response to an input from a keyboard for each melody note. The circuitry for such electronic musical instruments can now be built on integrated circuit chips so reduction of the cost and size of keyboards becomes more important for these instruments as it has for other electronic equipments.